Parametric modelling of neonatal mortality in relation to size at birth

Estimation of trajectory of protective efficacy in infectious disease prevention trials using recurrent event times

In studies of infectious disease prevention, the level of protective efficacy of medicinal products such as vaccines and prophylactic drugs tends to vary over time. Many products require administration of multiple doses at scheduled times, as opposed to one-off or continual intervention. Accurate information on the trajectory of the level of protective efficacy over time facilitates informed clinical recommendations and implementation strategies, for example, with respect to the timing of administration of the doses. Based on concepts from pharmacokinetic and pharmacodynamic modeling, we propose a non-linear function for modeling the trajectory after each dose. The cumulative effect of multiple doses of the products is captured by an additive series of the function. The model has the advantages of parsimony and interpretability, while remaining flexible in capturing features of the trajectories. We incorporate this series into the Andersen-Gill model for analysis of recurrent event time data and compare it with alternative parametric and non-parametric functions. We use data on clinical malaria disease episodes from a trial of four doses of an anti-malarial drug combination for chemoprevention to illustrate, and evaluate the performance of the methods using simulation. The proposed method out-performed the alternatives in the analysis of real data in terms of Akaike and Bayesian Information Criterion. It also accurately captured the features of the protective efficacy trajectory such as the area under curve in simulations. The proposed method has strong potential to enhance the evaluation of disease prevention measures and improve their implementation strategies.

Modelling non-linear patterns of time-varying intervention effects on recurrent events in infectious disease prevention studies

Protective efficacy of vaccines and pharmaceutical products for prevention of infectious diseases usually vary over time. Information on the trajectory of the level of protection is valuable. We consider a parsimonious, non-linear and non-monotonic function for modelling time-varying intervention effects and compare it with several alternatives. The cumulative effects of multiple doses of intervention over time can be captured by an additive series of the function. We apply it to the Andersen-Gill model for analysis of recurrent time-to-event data. We re-analyze data from a trial of intermittent preventive treatment for malaria to illustrate and evaluate the method by simulation.

Timing of birth and infant and early neonatal mortality in Sweden 1973-95: longitudinal birth register study

OBJECTIVE

To assess the impact of time of birth on infant mortality and early neonatal mortality in full term and preterm births.

DESIGN

Analysis of data from the Swedish birth register, 1973-95.

PARTICIPANTS

2 102 324 spontaneous live births of infants without congenital malformation.

OUTCOME MEASUREMENTS

Absolute and relative risk of infant mortality, early neonatal mortality, and early neonatal mortality related to asphyxia.

RESULTS

Infant mortality, early neonatal mortality, and early neonatal mortality related to asphyxia were higher in infants who were born during the night (9 pm to 9 am) compared with those born during the day for 1973-9, 1980-9, and 1990-5. The difference was more dramatic for preterm infants. The largest difference was observed during 1990-5, when there was a 30% increase in early neonatal mortality (relative risk 1.31, 95% confidence interval 1.10 to 1.57) and a 70% increase in early neonatal mortality related to asphyxia (1.70, 1.22 to 2.38) in preterm infants born during the night compared with rates for preterm infants born during the day. A detailed analysis over 24 hours revealed two "high risk" periods: between 5 pm and 1 am and around 9 am.

CONCLUSIONS

Infants born during the night have a greater risk of infant and early neonatal mortality and early neonatal mortality related to asphyxia than those born during the day. There has been no improvement over the past two decades. The problem is more serious for preterm births and was even worse in the 1990s. Shift changes and the hours immediately after such changes are high risk periods for neonatal care.